HETEROTRIMERIC G PROTEIN REGULATION OF TRANSPIRATION EFFICIENCY, STOMATAL DENSITY, AND PHENOTYPIC PLASTICITY IN ARABIDOPSIS THALIANA
Open Access
- Author:
- Nilson, Sarah Elisabeth
- Graduate Program:
- Plant Biology
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- June 12, 2009
- Committee Members:
- Sarah Mary Assmann, Dissertation Advisor/Co-Advisor
Sarah Mary Assmann, Committee Chair/Co-Chair
Paula Mc Steen, Committee Member
Andrew George Stephenson, Committee Member
David Eissenstat, Committee Member - Keywords:
- transpiration efficiency
Arabidopsis thaliana
Heterotrimeric G proteins
stomatal density
phenotypic plasticity - Abstract:
- Heterotrimeric G proteins are GTP-binding proteins that function in signal transduction in eukaryotes. Despite the relative paucity of genes which encode G protein subunits in plant compared to animal genomes, analysis of Arabidopsis thaliana and rice heterotrimeric G proteins mutants have revealed multiple and diverse roles for G proteins in plant physiology. These functions include environmental and hormonal signaling, cell division, development, and stomatal aperture regulation. The functions of heterotrimeric G proteins in Arabidopsis have been previously explored primarily via cell and molecular biology approaches with little emphasis on how G proteins contribute to whole plant water status and plant fitness. This work in this thesis investigates G protein function at the whole-plant level in attempt to understand this missing component of our knowledge of G protein function in plants. Chapters 1-3 are introductory chapters that explain in more depth the rational and organization of this thesis (Chapter 1) and review literature on the regulation of transpiration in Arabidopsis (Chapter 2) and G protein regulation of stomatal movements (Chapter 3). Chapter 4 identifies the sole Gα subunit in Arabidopsis, GPA1, as a positive regulator of transpiration efficiency, despite stomatal ABA sensitivities of gpa1 mutants that would suggest the opposite. GPA1 regulates transpiration efficiency in part via stomatal density control which modulates whole-leaf stomatal conductance. Chapter 5 is my attempt at understanding the molecular mechanism behind GPA1 regulation of stomatal density and development, by exploring potential biochemical interactions between GPA1 and previously identified proteins which function in stomatal development. Chapter 6 addresses the question, how do G proteins contribute to plant fitness? This chapter identifies the gene which encodes the sole Gβ subunit in Arabidopsis, AGB1, as a plasticity gene. AGB1 regulates phenotypic plasticity, the ability for one genotype to display different phenotypes under different environmental conditions, in response to water availability for a number of fecundity-related traits. Chapter 7 investigates whether G proteins also function in the regulation of cross-generational phenotypic plasticity, when the environment of the parent affects the phenotype of the offspring. In this study I found significant genetic variation for cross-generational among G protein mutants and wild type plants and that gpa1 and agb1 mutants had reduced, if not abolished, cross-generational plasticity for these traits compared to wild type. Chapter 8 discusses how this thesis contributes to plant biology and also suggests additional avenues of inquiry to further elucidate the results of the previous chapters.